1. Field of the Invention
This invention relates generally to hydraulic jacking devices and, more particularly but not by way of limitation, it relates to an improved apparatus for raising and supporting a foundation or concrete slab of a building by utilizing metal pilings driven to load supporting underground strata.
2. Description of the Prior Art
Houses and other buildings are often erected on foundation members or concrete slabs which are not in direct contact with stable, load supporting underground strata. If the initial construction of the foundation or slab is improper or if soil conditions change, settling of the foundation or slab may occur. This may result in major structural damage to the foundation members and to the building. If uncorrected, eventual collapse of the building may occur.
The prior art for correction of this type of problem includes numerous types of foundation jacking apparatus that utilize one or more powered jacks to place a support structure such as a metal piling beneath or adjacent to the sunken foundation. These prior types of apparatus are such that the piling is driven to a sufficient depth that it bears against bedrock or other subsurface body or that the piles experience sufficient skin friction to provide stable support for the foundation and building.
U.S. Pat. No. 2,982,103 provides an early teaching wherein a single hydraulic jack is used in-line with a pile to apply expansive force between a load plate and a subsurface load bearing earth structure. The plate is rigidly attached to the foundation wall thereby to adjust the wall level in accordance with hydraulic jack actuation. This patent discloses the basic method for underpinning of a building or foundation.
U.S. Pat. No. 3,796,055 discloses another apparatus and variation of method for carrying out foundation underpinning. This method uses hydraulic jacks within a pit that is formed alongside the foundation to be raised. A concrete pad is formed within the pit to provide a jacking base to support the hydraulic jack operation. U.S. Pat. No. 3,902,326 teaches apparatus having a single in-line hydraulic actuator that is disposed to drive a piling downward until it encounters bedrock or other firm footing. The jacking apparatus is firmly attached in support of the foundation and the foundation level can then be adjusted relative to the piling member support. U.S. Pat. No. 4,765,777 is a most recent teaching of foundation jack apparatus wherein two extended hydraulic actuators are each attached at one end to the foundation and at the other end to a yoke gripping a piling member and the actuator pistons are drawn inward while pulling the piling member and driving it downward into the earth to bedrock or substantial support.
While it is possible in some instances to drive the support pile into firm contact with actual bedrock, in many instances limitations in the placement apparatus or job site conditions allow for the pile to be driven to a depth short of actual bedrock. In these instances, a combination of the increased load bearing capability of the subsurface strata reached by the end of the pile and skin friction between the pile and surrounding strata (reference U.S. Pat. No. 4,070,867) are relied upon to support the pile which in turn supports the foundation and building. In these cases it is advantageous to increase the number of piles used to support the foundation so as to distribute the total load, thus guarding against future settling of the foundation in the event of slight changes in the subsurface conditions. Prior art techniques would require additional apparatus to be used so as to place additional piles singularly. The present invention overcomes the limitations of prior art apparatus by simultaneously driving two pile members in parallel using one apparatus.